Data source encoding reduces the amount of bandwidth and resources required for transmission of a particular data source. Significant reductions are achieved by compression, especially in data sets exhibiting patterns. Image data and speech data are two exemplary data types upon which data source encoding is especially useful. Both produce large quantities of data that exhibit patterns rendering possible an efficient compression.
Quantization schemes used for data source encoding evaluate a data source for rendering an intelligent encoding of the data based upon the statistics of the data source. Conventional data source encoding schemes design a quantizer using a large database of the source known as the training data. The training data is typically selected to encompass all possible statistics of the data source, i.e., the transmission encoded data. The balance in designing a succesful quantizer is a balance between performance and complexity. However, when the quantizer is designed to perform reasonably well for all possible source statistics, it will not be optimal for a given realization of a source.
Other problems are unaddressed by conventional quantization data source encoding schemes. The conventional schemes are not able to adapt with time-varying statistics of a data source. In addition, bandwidth efficient adaptation is generally unfeasable due the enormous memory costs associated because it would be typically necessary to store data from the beginning of transmission to adapt the quantizer to the current statistics of the source. Then, even if the quantizer can be modified to depict current statistics of the source, it would typically be necessary to transmit the entire data encoding codebook to the receiver. This is a prohibitive bandwidth expense. Such conventional schemes do not provide for the possibility of variable rate encoding that holds promise in wireless code division multiple access (CDMA) communication environments.
Many quantization encoding schemes also have considerable computational and search complexity in the nonadaptive case. The memory and computation costs of vector quantizers grows exponentially with bit rate. Such costs have lead to the employment of sub-optimal quantizers even for sources with large databases to provide sufficient statistical information for optimal quantization.